In general, when using electric power as a heat source for roasting coffee beans, the heat source for roasting 1 kg of coffee beans needs 14 to 20 KW. Thus, if the weight of coffee beans to be roasted is 1 kg or more, gas heating (for example, propane gas and LNG gas) is almost always used. However, gas heating typically requires an expert to predictably roast coffee beans to an predetermined degree.
Further, an important know-how for roasting coffee beans is to find certain points when a first crack sound is generated upon applying the heat to green beans, wherein the first crack sound is failed by reducing the heat after a while, and when the heat is further reduced after a second crack sound is generated again so that the beans have a desired color.
As described above, since the technique of roasting coffee beans is largely depended upon the expert's experience and skill to find the points of the first, second, and third crack sounds and requires increasing or reducing the heat while observing and heating the roasted coffee beans, it generally very difficult, if not even impossible for an inexperienced user to predictably and reliably roast coffee beans to a desired state. Even though new machines for roasting coffee beans using hot air have been developed, resulting roasted coffee is often not satisfactory for the general public. Thus, the coffee roasting industry largely relies on expert roasters.
Further, when roasting the coffee beans, a considerable amount of smoke is generated, which is in heretofore known devices typically discharged to the outside by installing a smoke pipe, or eliminated by installing a large smoke collector (often 5 to 6 times larger as the roasting machine) above the device in combination with an after-burner for burning the smoke collected in a smoke reserve tank (which is also six or more times as large as the roasting machine). Therefore, a very large space is required to roast coffee beans using heretofore known devices. Moreover, a smoke pipe is often essential to discharge the burned gas placing further restriction to general use. Consequently, coffee bean roasting is generally performed only in factories or smaller roasting operations, even when roasting a small amount (several kilogram) of coffee beans.
Therefore, there is still a need to provide improved coffee roasting devices that will allow fully automated operation by an inexperienced user or even novice at significantly reduced power consumption.